This invention relates to a system for cooling hypersonic aerospace vehicles subjected to high thermal loads and is particularly directed to the provision of a structure for cooling and insulation of such aerospace vehicles employing cryogenic fuels.
Various arrangements have been provided for cooling surface portions of aerospace vehicles, particularly hypersonic aerospace vehicles. In the design of thermal protection systems for aerospace vehicles, such system should not transfer excessive heat to the basic vehicle structure. should have low weight, and should produce low thermal stresses. Current thermal protection system concepts employ multitudes of ceramic tiles as reusable surface insulation to accommodate thermal expansion differences with the structure and multitudes of joints resulting in considerable undesirable weight. Such tiles have the further disadvantages of being weak, brittle and subject to surface cracking and being labor intensive, both for production and for maintenance.
Various thermal protection systems, and particularly systems for cooling surface portions of an aircraft, have been developed in the prior art to overcome these problems and to provide suitable cooling for the exterior surface portions of an aerospace vehicle. Thus, U.S. Pat. No. 4,344,591 is directed to a multiwall thermal protection system to replace the tile system of the prior art.
In another form of cooling system employed in the prior art, the fuel employed in the aircraft is circulated in heat exchange relation with external surface portions of the aircraft to cool such portions, prior to delivery of the fuel to the aircraft power plant. Thus, U.S. Pat. No. 3,015,461 discloses, in an airplane, a fuel transfer means from the fuel supply, including a heat exchanger section located in heat exchange relation to an exterior surface of the aircraft for circulation of liquid fuel therethrough, to effect surface cooling required by supersonic surface heating conditions. The increase of fuel temperature as the liquid fuel circulates through the heat transfer section prior to delivery of the fuel to a thrust augmentation system, such as an afterburner, adds to the effectiveness of the latter. In one modification of the arrangement of this patent, a heat transfer section is located in the wing adjacent an exterior surface portion of the airplane and formed of a plurality of passageways for the fuel. The interior of the wing functions as a fuel storage member for the fuel, usually in the form of a petroleum distillate fuel, such as those designated JP4 or JP5.
In the 3,015,461 patent, the means forming the heat exchange passages 44, 48 and 53 for the fuel, in FIGS. 5-7 of the patent, are not an integral part of the structural design of the airplane and do not form load bearing members. The skin of the airplane in effect forms a heat exchanger. The patent also does not address the problems presented where a liquefied gas at very low temperatures, such as liquid hydrogen, is employed as the fuel. Under these circumstances, one of these problems is that when the aircraft is standing on the runway, and if there is insufficient insulation, liquid air is formed on the skin of the vehicle or on the outside of the fuel tank, resulting in an extremely hazardous condition.
It is accordingly an object of the present invention to provide an improved heat exchange structure for cooling portions, particularly external portions, of an aircraft, such as a hypersonic aerospace vehicle, and wherein the heat exchange structure is a load bearing structure.
Another object of the invention is to provide a simple, durable load bearing cooling structure of the above type which can be readily fabricated and which is adapted for use with cryogenic fuels, such as liquid hydrogen.
A further object of the invention is the provision of an improved cooling and insulation system for aerospace vehicles, particularly supersonic aerospace vehicles, which is formed integral with an airframe component, such as the fuselage, wing or tail of the aerospace vehicle, for use with liquid cryogenic fuel, and which can be subjected to a vacuum when the vehicle is on a runway, to prevent hazardous formation of liquid air on the outer skin or other components of the vehicle and to minimize heat flow into the tank and its cryogenic fuel.